Field
The present disclosure relates to the field of molds for molding and vulcanizing a tire tread. More specifically, the invention relates to the molds used for molding in the tread blocks which are partially or completely covered by a cover layer.
Description of Related Art
It is known practice to design tires the tread of which comprises various rubber compounds. Document WO 03089257 discloses such treads. More specifically, document WO 03089257 discloses a tread comprising tread blocks the walls of which are covered with a cover layer. The material of which this cover layer is made differs from the rubber compound of which the tread is made. This material notably has much better wet grip than the wet grip of the rubber compound. This allows a very significant improvement in cornering performance on wet ground.
One way of manufacturing this tread is notably disclosed in document WO 2006069912. According to this method of manufacture, in a first step, provision is made for the material intended to constitute a cover layer to be injected in the form of one or more inserts into the green tire using an injection nozzle. The insert or inserts is or are then shaped, in a second step, by ribs of a vulcanizing mold so that they cover all or part of the walls of the grooves molded by these ribs.
This method of manufacture has its limits, particularly as far as obtaining precision moldings is concerned. Specifically, during the shaping thereof, the insert experiences a significant shear force from the rib in order to convert this insert into a layer of lesser thickness. This shear force may cause cracking within the insert, making it more difficult to control the movements of the material of which this insert is made. The shape and the thickness of the cover layer thus formed may therefore be somewhat haphazard. The advantages afforded by the additional layer to the performance of the tire are then reduced.
In addition, in this method of manufacture, it is necessary to make the inserts align with the ribs. This makes manufacture of the tread more complicated.
There is therefore a need to improve the incorporation of a cover layer on the walls of tread blocks of a tire tread.